1. Field of the Invention
The present invention relates to a method for transmitting optical burst data by inserting new burst data into a void between the optical burst data on a channel so as to reduce errors of the optical burst data and improve availability of the channel over an optical burst switching (OBS) network.
2. Description of the Related Art
Over optical burst switching (OBS) networks, typically, IP packets coming into an optical domain are aggregated to burst data at an edge node, and such burst data is routed to their destination nodes via a core node according to their destinations or quality of service (QoS). A burst control packet (BCP) and a payload (burst data:BD) are separated by an offset time and transmitted on different channels. In more detail, the BCP precedes the burst data by the offset time to reserve in advance a path for the transmission of the burst data. Accordingly, the burst data can be transmitted over the optical network without buffering. Hereafter, the transmission of the optical data is explained in reference to FIG. 1.
FIG. 1 illustrates nodes that transmit and receive or switch the burst data over the OBS network, which is described in detail.
As for incoming IP packets, the node A 100, which is an edge node, generates burst data by aggregating the IP packets. Edge nodes 100, 106, and 108 serve to generate and transmit optical burst data packets by aggregating IP packets, or receive the optical burst data packets and divides them into IP packets. Core nodes 102 and 104 are responsible to optically switch the optical burst data. Upon generating the burst data in a desired size, the node A 100 generates and transmits a burst control packet (BCP) to the node B 102 which is the core node. After the offset time, the node A 100 transmits the burst data to the node B 102. The BCP contains information relating to a destination address and a source address of the burst data, a size of the burst data, and the offset time.
The node B 102 checks the destination address of the burst data to be received from the received BCP, determines an optical path, and reserves a time for the optical switching. While the BCP is converted optic-electronically or electro-optically at the node B 102, the burst data follows the optical path only by the optical switching, without the optic-electronic conversion. The node B 102 can optically switch the burst data to the node D 106 or the node C 104 depending on whether the destination of the burst data provided from the node A 100 is either the node D 106 or the node E 108.
It has been described that the node B 102 relays the burst data from the node A 100 to either the node D 106 or the node E 108. Meanwhile, the node B 102 may be the destination of the burst data originated from the node A 100 or may generate burst data to be transmitted to the node D 106 or the node E 108. In other words, the node B 102 being the core node can function as the edge node. In this case, a method is demanded for the node B 102 to relay the burst data received from the node A 100 to the node D 106 or the node E 108 on one channel by inserting its generated burst data between the received burst data so as to save resources.
FIG. 2 illustrates transmission of the BCP and the burst data over a conventional OBS network. Descriptions are provided of a problem occurring when the void between burst data is filled with other burst data on a conventional channel in reference to FIG. 2.
Referring to FIG. 2, the BCP is transmitted and received on a channel λBCP, and the burst data BD is transmitted and received on a channel λBD. As mentioned earlier, the BCP contains information relating to the offset time and the BD size. The offset time is a temporal difference between the receiving time point of the BCP and the receiving time point of the BD.
In FIG. 2, the offset time between the BCP1 and the BD1 is T_offset1, and the offset time between the BCP2 and the BD2 is T_offset2. The channel λBD is not filled with the burst data all the time, but a non-transmission time period without data signals is present between the burst data, which is called a void time T_void.
A node performs the optic-electronic conversion and electrical processing to the received BCPs. As for the BDs, the node conducts switching or add/drop function. The node may have data ready to be transmitted on the same channel as the channel of the BD1 and the BD2. In FIG. 2, it is exemplified that the node transmits the BD3 on the same channel as the BD1 and the BD2. The node serves as the core node with respect to the BD1 and the BD2. Yet, the node serves as the edge node for the BD3. When the BCP3 and the BD3, which are locally generated without the offset time, are transmitted from the node, the BCP3 precedes the BD3 by the offset time T_offset3. In case that the BCP3 and the BD3 are transmitted from another node, rather than generated locally, the BCP3 and the BD3 are received at the node with the offset time defined from the very first.
However, a general node in the OBS network cannot learn the size of the time interval T_void between the BD1 and the BD2 until the BCP2 is input. In this regard, when T_void is longer than the BD3 regardless of the input of the BCP2, a method is demanded to fill the time interval between the BCP1 and the BD1 with the BCP3 and the BD3, respectively, without collisions with other BDs.